Temperature Dependent Dynamic Strain Localization and Failure of Ductile Polymeric Rods under Large Deformation

Ductile polymers have been increasingly applied in engineering applications to enhance the structural reliability under impact loading. Due to the limitation of experimental setup to achieve large tensile deformation and the difficulty to achieve dynamic force equilibrium, the localization and post-necking stages up to fracture of ductile polymers at high strain rates have less been investigated. In the present work, the dynamic strain localization of ductile polymeric rods under large tensile deformation up to fracture is studied on the bespoke Hopkinson tension bar synchronized with a high-speed camera. Transparent polycarbonate (PC) is used as a model material in the present study. Likewise, the constitutive response and fracture behaviour of polycarbonate are also characterized with the assistance of Digital Image Correction (DIC) from low to high strain rates under various temperature conditions. The results quantitatively show that the dynamic local strain rate initially increases dramatically to 200 % of the nominal strain rate due to strain localization. This is followed by a rapid drop with necking propagation, and finally tends to stay at strain rate of approximately 20 % of the nominal strain rate until fracture. The elevated temperatures would result in higher local strain rates. Two constitutive models with and without the consideration of constant strain rate condition are constructed for PC and incorporated in finite element simulations. The trend of dynamic local strain rate history with respect to nominal strain rate is successfully reproduced in simulations. The constitutive models particularly the simple dynamic amplification model, are able to reflect the phenomenological key features of the experimentally observed macroscopic and local responses of polycarbonate, and would find their potential applications in impact resistant transparency design.